I am looking for a way to check if 2 permutations (represented by lists) are of the same parity. Note that I am not interested if they are even or odd parity, just the equality.
I am new to Python and my naive solution is given below as a reply. I am looking forward to Python gurus showing me some cool tricks to achieve the same in lesser, more elegant Python code.
A minor variant of the previous answer - copy perm1, and save array lookups.
def arePermsEqualParity(perm0, perm1):
"""Check if 2 permutations are of equal parity.
Assume that both permutation lists are of equal length
and have the same elements. No need to check for these
conditions.
"""
perm1 = perm1[:] ## copy this list so we don't mutate the original
transCount = 0
for loc in range(len(perm0) - 1): # Do (len - 1) transpositions
p0 = perm0[loc]
p1 = perm1[loc]
if p0 != p1:
sloc = perm1[loc:].index(p0)+loc # Find position in perm1
perm1[loc], perm1[sloc] = p0, p1 # Swap in perm1
transCount += 1
# Even number of transpositions means equal parity
if (transCount % 2) == 0:
return True
else:
return False
My naive solution:
def arePermsEqualParity(perm0, perm1):
"""Check if 2 permutations are of equal parity.
Assume that both permutation lists are of equal length
and have the same elements. No need to check for these
conditions.
"""
transCount = 0
for loc in range(len(perm0) - 1): # Do (len - 1) transpositions
if perm0[loc] != perm1[loc]:
sloc = perm1.index(perm0[loc]) # Find position in perm1
perm1[loc], perm1[sloc] = perm1[sloc], perm1[loc] # Swap in perm1
transCount += 1
# Even number of transpositions means equal parity
if (transCount % 2) == 0:
return True
else:
return False